An engine may include a knock control system to mitigate engine knock. The knock system may retard spark timing of a cylinder that is exhibiting knock to reduce the possibility engine degradation. The spark timing for the cylinder may be subsequently advanced when knock is suppressed to increase engine efficiency. The advance rate of spark is a constant value. Advancing spark timing after retarding spark timing may lead to further indications of engine knock if the spark advance rate is too high. On the other hand, engine fuel economy may degrade if the spark advance rate is too low. Therefore, it may be desirable to provide a way of adjusting spark timing advance rate that improves engine efficiency, but does not lead to engine knocking in a short time period.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: judging if knock is present in a cylinder combusting air and fuel via receiving an input to a controller; adjusting, via the controller, a rate of spark advance is supplied to the cylinder after knock is judged present in the cylinder in response to a way the cylinder was previously deactivated.
By adjusting a rate of spark advance supplied to a cylinder after knock is judged present in the cylinder in response to a way a cylinder was previously deactivated, it may be possible to provide the technical result of improving engine fuel economy while mitigating engine knock. For example, engine cylinders may be deactivated via ceasing fuel flow to the cylinders while the cylinder's intake and exhaust valves continue to operate or by other methods described herein. Air flowing through the cylinders cools the cylinder at a fast rate. If a driver rapidly increases a torque request and knock results, spark timing may be retarded to control the knock. However, the spark advance rate may be set to a higher level since the cylinder has cooled and it may be expected that knock may be slower to return. Conversely, if engine cylinders were deactivated by ceasing fuel flow to the cylinders and closing intake and exhaust valves over an engine cycle, engine cylinders may not cool very fast since flow through the cylinders is restricted. If a driver rapidly increases a torque request and knock results under these conditions, spark timing may also be retarded to control the knock. Nevertheless, the spark advance rate may be set to a lower level since the cylinder has not cooled as much as if the cylinders were deactivated with operating valves. As a result, it may be expected that knock may return faster. Reducing the spark advance rate may reduce the possibility of engine knock returning after spark has been retarded in response to an earlier knock event.
The present description may provide several advantages. For example, the approach may improve vehicle fuel economy. Additionally, the approach may reduce the possibility of reoccurring engine knock after a knock event. Further, the approach may improve vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.